Process for preparing pitch bound aggregate

ABSTRACT

IMPROVED PROCESS FOR PRODUCING BOUND AGGREGATE WITH A THERMOSETTING BINDER COMPRISING A MODIFIED PETROLEUM PITCH PLASTICIZER AND POWDERED PITCH, USEFUL EXAMPLE, IN PRODUCING REFRACTORY LININGS AND CARBON ELECTRODES.

United States Patent O 3,689,299 PROCESS FOR PREPARING PITCH BOUND AGGREGATE Lloyd H. Brown, Crystal Lake, and David ll). Watson,

Barrington, Ill., assignors to The Quaker Oats Company, Chicago, Ill. No Drawing. Filed Mar. 16, 1971, Ser. No. 124,983 Int. Cl. C08h 13/00, 17/02; C09d 3/24 US. Cl. 106-284 1 Claim ABSTRACT OF THE DISCLOSURE Improved process for producing bound aggregate with a thermosetting binder comprising a modified petroleum pitch plasticizer and powdered pitch, useful for example, in producing refractory linings and carbon electrodes.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to a process for binding aggregate by solubilizing powdered pitch at the surface of the aggregate with a modified petroleum pitch plasticizer.

Background of the invention Because of the widespread commercial availability, and because of the attractive chemical properties of pitch, particularly coal tar pitch softening above 100 0, these materials are highly attractive materials for use as binders or coating materials. One difiiculty with these pitches is that they are solids at room temperature and at most temperatures at which they can be worked conveniently. Consequently, use of these pitches as a binder for aggregate is difiicult since the unmodified pitches must be heated to relatively high temperatures before effective coating of the aggregate particles by the pitch will take place. Furthermore, unmodified pitch bound aggregate has the disadvantage of softening when heated above the softening point of the pitch. This is undesirable because the pitch bound aggregate tends to sag, slump, or distort at elevated temperatures.

Satisfactory monomeric furan pitch binders have been suggested. These binders are workable at room temperature or at nearly room temperature, are converted to a thermoset condition in the presence of a catalyst, and give high Conradson carbon values. Specifically, a monomeric furfural and cyclohexanone or aliphatic ketone modified coal tar pitch binder has been suggested. A monomeric furfuryl alcohol, furfural, cyclohexanone and/or mesityl oxide petroleum or coal tar pitch binder has also been suggested.

Monomeric furan modified coal tar pitch binders give higher Conradson carbon values than binders made with petroleum pitch of a similar softening point, but binders made with coal tar pitch have higher initial viscosities and suffer greater increases in viscosity on standing than binders made with petroleum pitch of a similar softening point.

For example, binders made with coal tar pitch are only compatible up to 40 percent by weight of furfural-cyclohexanone, but compatible petroleum pitch binders can be made with as much as 70 percent by weight of furfuralcyclohexanone. The advantage in using higher amounts of furfural-cyclohexanone is that the initial viscosity of the modified petroleum pitch binder is lower. This makes the modified binder more workable at room temperature. Since the modified petroleum pitch binder has such a low initial viscosity even when it is cooled to below freezing, it is still of a low enough viscosity to be easily distributed. Since many refractory brick plants are poorly insulated,

3,689,299 Patented Sept. 5, 1972 the viscosity of the modified binders at lower than room temperature is very important.

The seemingly impossible problem was how to provide a modified pitch binder which had all the advantages of prior art monomeric furan pitch binders but which gives Conradson carbon yields approaching those of a furan modified coal tar pitch and, which at the same time, has a low initial viscosity and is workable at below room temperature, and which does not increase in viscosity at a substantial rate on storage.

SUMMARY OF THE INVENTION It is an object of this invention to provide a process for producing bound articles from modified pitch binders which are converted to a thermoset condition in the presence of a catalyst.

Another object of this invention is to provide a process wherein the binder gives high Conradson carbon yields.

Still another object of this invention is to provide a process wherein the modified pitch plasticizer has a low initial viscosity, does not increase substantially upon cooling to freezing, and does not increase in viscosity at a substantial rate on storage.

The objects of this invention are accomplished by a process for binding aggregate with a modified pitch binder which comprises:

(a) blending 30 to parts by weight of petroleum pitch with 70 to 20 parts by weight of monomeric dispersants, wherein said dispersants are furfural and cyclohexanone or methyl aliphatic ketones having a formula:

wherein R is a hydrocarbon group having between 2 and 6 carbon atoms;

(b) heating the blend to solubilize the petroleum pitch in the dispersants and to produce a homogeneous plastlcizer;

(c) admixing aggregate with said plasticizer, an acidic or basic catalyst, and 0.6 to 2. percent by weight of pow dered pitch;

(d) forming the admixture into a desired shape; and

(e) curing the formed admixture.

Of particular importance to our invention is the use O f a monomeric furan modified petroleum pitch plastlclzer having a viscosity of less than 1000 cps. (centipoises) at 27 C. in combination with powdered pitch, preferably powder coal tar pitch. The prior art teaches away from the contacting of powdered pitch with the aggregate without first liquifying it with plasticizer or by heat. One remarkable feature of our invention is that it provides a bound aggregate which has none of the disadvantages of an unmodified pitch bound aggregate. An other feature is that it provides a product which has a Conradson carbon value similar to that of a furan modified coal tar pitch binder, and, at the same time, the process provides a modified petroleum pitch plasticizer which is easily workable at room temperature and below and which does not substantially increase in viscosity upon standing in storage.

By the word pitch we mean to include both pitches derived from coal and from petroleum. The words coal tar pitch and petroleum pitch in the present specification are used in the same manner as in the prior art. A preferred type of petroleum pitch possesses a softening point (ASTM Standard Test D-36-64T, Ring and Ball Test) from about 240 to about 300 F., and a Conradson carbon value (ASTM Standard Test D-24l6) from about 48 to about 60 percent by weight. A preferred type of coal tar pitch has a softening point from about to about C., and a Conradson carbon value from about 60 to about 80 percent by weight.

The methyl aliphatic ketones useful in this invention are compounds of the formula:

where R is a hydrocarbon group having between two and six carbon atoms. The monovalent hydrocarbon group may have aliphatic unsaturation but aliphatic unsaturation is not essential. Suitable hydrocarbon groups include both straight and branched chains. Examples of satisfactory hydrocarbon groups are the following:

It is essential that the homogeneous modified petroleum pitch plasticizer used in this invention contain 30 to 80 parts by weight of petroleum pitch and 70 to parts by weight of a combination of furfural and cyclohexanone or methyl aliphatic ketones as dispersants. If more than 70 parts by weight of furfural and cyclohexanone or methyl aliphatic ketone is used with the petroleum pitch, it is diflicult and in most cases impossible to make a plasticizer which is compatible at room temperature. By compatible we mean that the composition is homogeneous and does not separate into different phases at the specified temperature. If less than 20 parts by weight of furfural and cyclohexanone or methyl aliphatic ketone is blended with the petroleum pitch, it is generally impossible to provide a plasticizer which has a viscosity of 27 C. of less than 1000 cps. We regard it as a highly desirable feature of our process that the plasticizer have a viscosity at 27 C. of less than 1000 cps. If the plasticizer has an initial viscosity when it is first made of less than 1000 cps., it is very workable since it easily wets out the powdered pitch and the aggregate. Furthermore, a furan modified petroleum pitch plasticizer having an initial viscosity of less than 1000 cps. at room temperature also has a sufficiently low viscosity at below room temperature (e.g. 10 F.) to be workable without warming.

The amount of furfural in proportion to the amount of methyl aliphatic ketone or cyclohexanone in the plasticizer is not narrowly critical. It is preferred that the furfural and the cyclohexanone or methyl aliphatic ketone be in a ratio of l to l to 2 to 1 when the catalyst is basic and the aggregate neutral or basic. No commensurate advantage is gained by using relative amounts other than those described above.

It has been found advantageous when the catalyst is acid and the aggregate neutral or acidic, to use mixtures of furfuryl alcohol and furfural in place of furfural as the monomeric furan portion of the dispersant. The amount of furfuryl alcohol in proportion to the amount of furfural and cyclohexanone or methyl aliphatic ketone is also not narrowly critical. We have found that the furfural, furfuryl alcohol, and cyclohexanone or methyl aliphatic ketone can be in a ratio of 1:1:1 to 2:0.5zl. While other relative amounts may be used, no commensurate advantage is gained thereby. It is preferred that the furfural, furfuryl alcohol, and cyclohexanone or methyl aliphatic ketone be in the ratio of 1: 1:1.

To prepare the furan modified homogeneous plasticizer used in this invention it is essential that the petroleum pitch, furfuryl alcohol and/or furfural, and cyclohexanone and/or methyl aliphatic ketone be blended to gether. It is also essential that the blend be heated for a time at a temperature sufficient to solubilize the petroleum pitch whereby a homogeneous petroleum pitch plasticizer is produced. The time and temperature necessary to solubilize the petroleum pitch in the monomeric dispersants will vary with the softening point of the petroleum pitch, the source of the petroleum pitch, the total amount of monomeric dispersants, and the relative amounts of the several monomeric dispersants. Excessive heats should be avoided to prevent premature polymerization of the plasticizer. While the parameters of time and temperature necessary to solubilize the petroleum pitch in the monomeric dispersants cannot be generally stated, they are easily determined by one skilled in the art. For example we have found that solubilization of the pitch in the monomeric dispersants can be achieved by gradually raising the temperature of the blend from ambient to 35 C. to 60 C. over a period of several liourse, for example 4 hours. While the time necessary to produce a homogeneous plasticizer is largely a function of the composition of the blend, it is also a function of the effectiveness of the stirring of the blend during the process of solubilizing the petroleum pitch in the monomeric dispersants.

The homogeneous plasticizer along with a catalyst is admixed with the aggregate. While the order of mixing is not critical, it is preferred to mix the aggregate and catalyst first. To this mixture, the modified pitch plasticizer is added. Another method is to mix the catalyst, aggregate, and modified pitch plasticizer all at once.

The aggregate selected will depend upon the particular application intended for the bound aggregate. If the bound aggregate is to be used as a core in foundry applications, then the aggregate selected can be any of the well-known core forming materials, such as quartz, silica sand, zirconium oxide, sea sand, bank sand, lake sand, reclaimed molding sand, olivine, chromite, and the like. If the bound aggregate is to be used in refractory applications, then the aggregate will be selected from carbon and from non-combustible materials such as metal oxides. These oxides, in turn, may include alumina, zirconia, magnesia, zircon, chrome ore, chromium oxide, and deadburned dolomite. Mixtures of the various materials may, of course, also be used.

The size of the particles of aggregate is not at all critical and may comprise any of those commonly used in the art. As an example, particle sizes may vary from pieces as large as one-half inch in cross section down to finely ground particles passing through a two hundred mesh [15. Standard sieve. Particles of ditferent sizes are sometimes used jointly as is known in the art.

The amount of plasticizer used on the aggregate and powdered pitch depends in well-known ways on the surface area, porosity, shape, etc., of the aggregate particles. For economical reasons, no more binder need be used than to dampen the aggregate and powdered pitch and to effectively bind the aggregate particles together. For example, if the aggregate is finely divided graphite or carbon the amount of plasticizer may be as high as 35 percent by weight based on the weight of the aggregate. If the aggregate is sand for example, we have found that only 0.5 to 2 percent by weight plasticizer based on the weight of the sand is necessary to effectively bind the aggregate particles together.

We also use between 0.5 and 2 percent by weight of powdered pitch with the aggregate. If less than 0.5 percent is used, the Conradson carbon values will be too low. If more than 2 percent by weight is used, the modified petroleum pitch plasticizer will not sufiiciently solubilize the powdered pitch at the surface of the aggregate.

Acids and bases commonly used in the art are used as catalysts in this invention. Suitable acid catalyst include inorganic and organic acids such as hydrochloric acid, sulfuric acid, nitric acid, orthophosphoric acid, benzene sulfonic acid, toluene sulfonic acid, naphthalene sulfonic acid, maleic acid, oxalic acid, malonic acid, phthalic acid, lactic acid, and citric acid. Suitable acid catalysts also include Friedel-Crafts type catalysts such as ferric chloride, aluminum chloride, and zinc chloride. Suitable acid catalyst include organic anhydrides such as maleic anhydride and phthalic anhydride. Examples of further satisfactory conventional acid catalysts include mineral acid salts of urea, thiourea, substituted ureas such as methyl urea and phenyl thiourea; mineral salts of ethanol amines such as mono-, di-, and triethanolamine; and mineral acid salts of amines such as methyl amine, trimethyl amine, aniline, benzylamine, morpholine, etc. Preferred acid catalyst have a K of at least Suitable base catalysts include alkali hydroxides such as lithium hydroxide, sodium hydroxide, potassium hydroxide, and the like; and alkaline earth hydroxides such as magnesium hydroxide, calcium hydroxide, and the like. Other satisfactory base catalysts include for example, amine catalysts such as primary amines like ethyl amine, propyl amine, etc.; secondary amines like diisopropyl amine, dimethylamine, etc., and tertiary amines like triisobutyl amine, triethylamine, etc. Examples of other satisfactory base catalysts are mixtures of mineral bases and amines such as a mxiture of sodium hydroxide and tri-n-butylamine; and mixtures of strong and weak mineral bases such as mixtures of sodium hydroxide and calcium hydroxide. Preferred basic catalysts have a K of at least 10- It is preferred that a basic catalyst be used when the monomeric furan component of the dispersant is furfural and an acidic catalyst is preferred when the furan component is a combination of furfural and furfural alcohol. The nature of the aggregate will also influence the choice of catalyst. For example, if the aggregate is alkaline, the basicity of the aggregate will neutralize an acid catalyst and inhibit satisfactory cure. An acid catalyst may also have a deteriorating effect on the alkaline aggregate. It is therefore preferred that an acidic catalyst be used with an acid or neutral aggregate and that a basic catalyst be used with an alkaline aggregate. Examples of an acidic or neutral aggregate are sand, graphite, carbon, etc. Examples of a basic aggregate are dolomite and magnesite.

The amount of the catalyst will vary with the type of aggregate and the curing time desired. For example, sand with a high clay content may have a high acid demand and require more acid catalyst. In general, the more catalyst the more rapid the cure. It is usually undesirable to have too rapid a cure since the workable life of the uncured but bound aggregate will be too short. The amount of catalyst can be easily determined by one skilled in the art. For example, we have found that for most purposes to 50 percent by weight of catalyst based on the weight of the modified petroleum pitch plasticizer is adequate when the aggregate is sand.

The binder of this invention may be cured at room temperature 0.). However, articles produced by the process of this invention which are cured by gradually raising the temperature from room temperature to 250 C. over several hours have greater strength. The rate of temperature increases is largely a function of the size of the bound article to be cured. Large articles must be heated at a slower rate of temperature increase than small articles in order that the temperature be uniform throughout the article and thus harmful internal stresses caused by uneven heating of the article be avoided. Exemplary rates for given samples are set forth in the examples below. Cured articles when the aggregate is magnesite or dolomite are suitable as refractory linings.

The process of this invention can further comprise pyrolyzing or graphitizing the binder when the aggregate is refractory material by heating the bound article to higher temperatures according to well understood procedures. For example, the binder may be pyrolyzed by heating the cured admixture of powdered pitch, plasticizer, catalyst, and refractory aggregate in a non-oxidizing atmosphere to a temperature of at least 800 C. to pyrolyze the binder and form a carbon bonded refractory product suitable, for example when the aggregate is carbon for carbon electrodes. The pyrolyzed admixture may then be heated in a non-oxidizing atmosphere to a temperature of 6 at least 2600 C. to graphitize the binder and form a graphitized refractory product.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following preferred embodiments of the invention are shown for the purpose of illustrating this invention and demonstrating the best mode for practicing the invention. It will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit and scope of the invention as it is more precisely defined in the subjoined claims.

Throughout the preferred embodiments the percentage coked retained weight of the binder was determined by ASTM Standard Test D2416 (Conradson Carbon Test) and the softening point of the pitch was determined by ASTM Standard D-36-64T (Ring and Ball Test). The viscosity of the plasticizers were measured with a Brookfield viscometer, LVF Model. The compressive strengths of the room temperature cured and tempered bound aggregate were determined with an Instron Tester at a head speed of 0.5 inch per minute. It is also to be understood that mesh size refers to the US. Standard Sieve Size. Where not otherwise indicated, percentages are weight percentages.

Example 1 Throughout this example, the modified pitch plasticizers were prepared in a two-liter three-necked flask which was equipped with a thermometer, condenser, mechanical stirrer, and a heating mantle. The monomeric dispersants comprising furfural and cyclohexanone were added to the flask and pitch was then added. The contents of the flask were stirred and the temperature was raised to 70 C. and held at that temperature for two hours, it was then raised to 90 C. and held at that temperature for two more hours. The resulting plasticizers were then bottled while hot and allowed to cool in loosely covered containers. The viscosities of the cooled plasticizers together with the composition of each plasticizer is given in Table I below:

TABLE I.VISCOSITY OF MODIFIED COAL TAR PITCH I PLASTICIZER v. VISCOSITY OF MODIFIED PETROLEUM PITCH PLASTICIZER 150 C. CTP 2 Percent by Weight F0 1 in 110 C. plasticizer CT 120 C. P 2 PP 3 1 F0 =Furfural-cyclohexanone in a 2:1 mole ratio. 1 OTP=Ooal tar pitch. 3 PP=Petroleum pitch. 4 Incompatible.

TABLE II.LOW TEMPERATURE VISCOSITY Temperature 1 Viscosity given in centipoises. 2 CTP of softening point 150 C. 3 PP of softening point 115 C.

4 Incompatible.

The stability of plasticizers prepared by the above procedure on storage along with the composition of the plasticizer are given in the following table:

TABLE III-STABILITY OF MODIFIED COAL TAR PITCH %&SZ'I]5IICgZERS v. MODIFIED PETROLEUM PITCH PLAS- Time interval Initial vlscosity 3 1 CTP of softening point 150 C. 9 PP of softening point 150 C.

3 Viscosity given in centipoises. 4 R.T.=Room temperature.

Example 2 Plasticizers containing pitch and having compositions indicated in the table below were prepared by the procedure of Example 1. Plasticizers containing only furfural and cyclohexanone were prepared by merely mixing these monomeric dispersants together.

Refractory mixes were prepared in a Clearfield Mixer, Model 150, from 4200 grams of magnesite aggregate +4 to -325 mesh, 252 grams of a combination as set forth in Table IV of plasticizer and powdered coal tar pitch (softening point 150 C.), and 13 grams of a powdered mixture of NaOH and Ca(OH) on carbon as catalyst. The aggregate, powdered pitch if any, and catalyst were premixed for two minutes to assure complete and uniform distribution. The plasticizer was then added and the materials were mixed for seven minutes.

The refractory mixes were then pressed into cylinders using a hardened steel mold. These cylinders measured 2" x 2". The cylinders were then carefully weighed to the nearest 0.1 gram.

Some of the cylinders were tempered before being tested for compressive set and weight loss and some were allowed to cure at room temperature. The cylinders which were tempered before testing were cured in a forced air oven using a twelve hour cycle. This cycle consisted of eight hours at 100 (3., two hours at 150 C., and two hours at 250 C. The room temperature cured cylinders were allowed to remain at room temperature (approximately 75 F.) for seven days before being tested.

The weight loss of the tempered cylinders was determined by reweighing the cylinders to the nearest 0.1 gram after they had returned to room temperature. The weight loss is based on the percentage weight difference between the initial weight of the cylinders and the weight of them after tempering.

The cylinders which were coked after they were tempered were buried in carbon in a covered metal box. The box was put into a Lindberg Electric Furnace and the temperature was gradually raised to 1800 F. over a period of six hours. The temperature was then held at 1800 F. for five hours. The furnace was then turned off and the box was allowed to cool in the furnace over a twelve hour period or until the cylinders could be handled. The percentage coked retained binder was then determined.

The tempered weight loss, coked retained binder, and room temperature and tempered compressive strength of cylinders prepared according to the above described procedures is given in the following table.

1 CTP of softening point 150 C. 2 1?]? of softening point 115 C.

Example 3 Following the procedure of Example 1 plasticizers having the composition given in the table below were prepared.

Refractory mixes following the procedure of Example 2 were made and tested. The results of the tests are also set forth in the following table.

TABLE V Total binder c0mposition, percent; Tempered Coked Total percent plasticizer Pow- Weight Retained dered Green loss, Denbinder, Den- FC PP 1 ECTP' density 3 percent sity a percent sity 3 1 PP of softening point 150 C. 1 CTP of softening point 115 C. Density=gramsleubie centimeter.

Example 4 Following the procedure of Example 1 but substituting furfuryl alcohol for part of the furfural, plasticizers were prepared having the compositions given in the table below.

Refractory mixes were prepared in a Clearfield Mixer, Model 150, from 4000 grams of calcined antracite +4 to -325 mesh, 1000 grams of a combination as set forth in the below table of plasticizer and powdered coal tar pitch (softening point 150 C.), and 50 grams of a 50 percent methanolic solution of p-toluene sulfonic acid as catalyst. The aggregate, powdered pitch, and catalyst were premixed for two minutes to assure complete and uniform distribution. The plasticizer was then added and the materials were mixed for seven minutes.

The refractory mixes were then pressed into cylinders using a hardened steel mold. These cylinders measured 27! X 2!!- The cylinders were then tempered in a forced air oven using a twelve hour cycle. This cycle consisted of eight hours at C., two hours at 150 C., and two hours at 250 C.

The cylinders were then coked. The coking process was accomplished by the following steps. The cylinders were buried in carbon in a covered metal box. The box was put into a Lindberg Electric Furnace and the temperature was gradually raised to 1800 F. over a period of six hours. The temperature was then held at 1800 F. for five hours. The furnace was then turned off and the box allowed to cool in the furnace over a twelve hour period. The percentage of coked retained binder was then determined. In each case the percentage coked retained binder where the plasticizer contained furfuryl alcohol was greater than where the plasticizer contained no furfuryl alcohol.

TABLE VL-TO'IAL BINDER COMPOSITION Total percent plastieizer Percent Powdered FL FA CY PP CTP l FL=Furfural.

i FA=Furfural alcohol.

a C Y=Oyelohexanone.

4 PP of softening point 150 C.

5 GTP of softening point C.

It is also demonstrated in Example 1 in Table II that modified petroleum pitch plasticizers have a lower initial viscosity and do not substantially increase in viscosity upon being cooled to low temperatures as compared with modified coal tar pitch plasticizers. The modified petroleum pitch plasticizers have such low initial viscosities that even when they are cooled to below freezing they can still be easily distributed on an aggregate.

Example 1 in Table III clearly shows the marked improvement in stability of the modified petroleum pitch binders over the modified coal tar pitch binders. Over a 30 day period, at both room temperature and 100 F., the modified petroleum pitch plasticizers advance in. viscosity at a considerably slower rate than modified coal tar pitch plasticizers. Even if the modified petroleum pitch plasticizers do advance in viscosity to even double their initial viscosity, their initial viscosties are so low that the binder is still very easily distributed over aggregate in the process of our invention.

The modified coal tar plasticizers of Example 1 are not used in the process of this invention but were reported to show that they are compatible with a lower amount of monomeric dispersants, have higher initial viscosities, and are not as stable as modified petroleum pitch plasticizers which are used in our process.

The principal purpose of Example 2 is to show that bound articles produced with a modified petroleum pitch plasticizer augmented with powdered coal tar pitch has a tempered weight loss and a percentage coked retained binder comparable to a prior art binder composed of a coal tar pitch solubilized in the same monomeric dispersants as used in the modified petroleum pitch plasticizer. The example also demonstrates that a modified petroleum pitch plasticizer augmented with powdered coal tar pitch has a lower tempered weight loss than a binder comprising powdered coal tar pitch which is not first solubilized by the monomeric dispersants but is mixed with the aggregate and then solubilized with the monomeric dispersants at the surface of the aggregate. Those articles made with palsticizers which do not contain petroleum pitch augmented with powdered pitch are not used in accordance with the process of this invention but were prepared to show the benefit above the prior art of practicing our process. Those articles made with plasticizers containing petroleum pitch which is augmented with powdered pitch show the tremendous benefit of practicing the process of our invention.

Example 3 demonstrates that when the monomeric dispersants comprise 50 percent by weight of the plasticizer that the best bound articles are produced when the ratio of plasticizers to powdered pitch is 1:1. Increasing the powdered pitch portion of the binder results in higher retained carbon values but the densities of the bound article are inferior to articles produced when the ratio 10 of plasticizer to powdered pitch is 1:1. All of the bound articles in this example are prepared by the process of this invention.

One purpose of Example 4 is to show that a plasticizer of this invention which contains furfuryl alcohol provides higher percentages coked retained binder when the catalyst is an acid catalyst than a plasticizer of this invention which contains no furfuryl alcohol.

From the foregoing description we consider it to be clear that the present invention contributes a substantial benefit to the art by proving a new, useful, and improved process for preparing pitch bound aggregates.

We claim:

1. 'In a process for binding aggregate with a modified pitch binder which comprises the steps of:

blending 30 to parts by weight of petroleum pitch with 70 to 20 parts by weight of monomeric dispersants, wherein said dispersants are furfural and cyclohexanone or methyl aliphatic ketones having a formula:

CH -CO-R wherein R is a hydrocarbon group having between 2 and 6 carbon atoms;

heating the blend to solubilize the petroleum pitch in the dispersants and to produce a homogeneous plas ticizer;

admixing aggregate with said plasticizer and an acidic or basic catalyst;

the improvement which comprises admixing 0.5 to 2 percent by weight of powdered pitch with the aggregate.

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